1. Field of the Invention
The present invention generally relates to a cleaning method for use in semiconductor device fabrication, and, more particularly, to a cleaning method for preventing or reducing defects and particles resulting from post-tungsten etch back or tungsten chemical mechanical polish.
2. Description of the Related Art
In semiconductor chip fabrication processing, it is well known that there is a need to clean the surface of the wafer after certain fabrication operations that leave unwanted residues or organic contaminants on the wafer surface. Examples of such fabrication operations include plasma etching (e.g., tungsten etch back (WEB)) and chemical mechanical polishing (CMP).
If unwanted residual materials or organic contaminants are left on the wafer surface during subsequent fabrication operations, this may cause inappropriate interactions between metallization features. In some cases, such defects may cause devices on the wafer to become inoperable. In order to avoid the undue costs of discarding wafers having inoperable devices, it is desirable to clean the wafer adequately, yet efficiently, after fabrication operations that leaves unwanted residue or contaminants on the wafer surface.
FIG. 1 is a schematic diagram illustrating unwanted residues or organic contaminants that remain on a wafer surface after a tungsten etch back or a tungsten chemical mechanical polish is applied in the conventional fabrication method to form a metal via.
A first layer 100, which may be a semiconductor substrate or a stack layer with a metal layer formed on a semiconductor substrate, is provided. A dielectric layer 105 is formed and patterned to form vias 110, which expose a portion of the first layer 100. A conforming metal barrier layer 115 is then formed on the patterned dielectric layer 105 and covers the profile of the vias 110, wherein the metal barrier layer 115 may include a Titanium nitride layer. A blanket metal layer 120, preferably a tungsten layer, is formed on the metal barrier layer 115 and into the vias 110, wherein the method for forming the tungsten layer 120 includes chemical vapor deposition (CVD). A tungsten etch back or tungsten chemical mechanical polish is performed to remove a portion of the tungsten layer 120 outside the vias 110 until the top surface of the tungsten layer 120 in the vias is close to the level of the top surface of the metal barrier layer 115, thus forming tungsten plugs 120a. Conventionally, the top portions of the tungsten plugs 120a are higher than the level of the top surface of the metal barrier layer 115 so as to avoid over polish or dishing of chemical mechanical polish. However, as the size of semiconductor devices shrinks, distances between adjacent tungsten plugs 120a also shorten. Thus, the top excess portions (dotted areas) of adjacent tungsten plugs 120a need to be removed to prevent the tungsten plugs 120a from contacting with each other and resulting in electrical short circuits.
Unwanted residues or organic containments (i.e. defects and particles) 125 produced during tungsten etch back or tungsten chemical mechanical polish may be left on the surface of the tungsten plugs 120a or the metal barrier layer 115. The defects and particles 125 remaining on the metal barrier layer 115 or the tungsten plugs 120a may provide a large resistance which affects the performance and the reliability of the device. Thus, the overall yield from the metal via fabrication process is reduced.
Traditionally, defects and particles 125 on the surface of the tungsten plugs 120a and the metal barrier layer 115 are removed by utilizing a DNS (Dai Nippon Screen brush) cleaner, which is used to brush clean the surface of the tungsten plugs 120a and the metal barrier layer 115. However, a problem with using the DNS cleaner is that it can scratch the surface of the tungsten plugs 120a and the metal barrier layer 115 while attempting to remove the residual particles or etching residue.
U.S. Pat. No. 5,804,091, granted Sep. 8, 1998, Lo et al., discloses a method of preventing defects and particles produced after tungsten etch back. The method includes utilizing an Ar plasma process, baking process, and D.I. water flushing with mega-sonic shaking to reduce defects and particles on the wafer surface. However, the method fails to reduce small-sized defects and particles 125 and fails to remove the top excess portion of the tungsten plugs 120a. 
In view of the foregoing, there is a need for a cleaning method for effectively removing particles, defects and top excess portions of the tungsten plug in post tungsten etch back or tungsten chemical mechanical polish operations.